Communication systems, especially wireless communication systems, have become an important portion of modern society. Generally speaking, in a wireless communication system, a base station (e.g., NodeB) establishes radio coverage over a cell, and a terminal (e.g., UE, user equipment) can therefore communicates with the base station by signal transmission through a wireless communication channel between the base station and the terminal. By different communication parameter combinations such as combinations of different modulation schemes and/or coding schemes, the communication channel, involving medium and environment where wireless signals transmit, can be separated to a plurality of physical channels for multiple-access. Some of the physical channels implement downlink channels for transmission from the base station to the terminal; others are allocated as uplink channels for transmission from the terminal to the base station. From another aspect, some of the physical channels are used for data transmission, and others are used for transmission of control information which is used for initiating, managing, handover and/or ending of the communication channel.
As a wireless communication system becomes more popular, the demand of higher throughput becomes more important. To fulfill throughput demand, the base station needs to provide the data service in an efficient way to accommodate various applications, e.g. voice service, data download, streaming, gaming, browsing, and etc, under the limited channel bandwidth. An efficient way to maximize the cell capacity is to allocate higher data rate to terminals with better channel qualities. In modern wireless communication systems, this concept is realized by adaptive modulation and coding scheme (adaptive MCS). The terminal shall monitor the downlink channel quality and report the quality metric, often referred to as channel quality indicator (CQI), to the base station. Then the base station can schedule proper data transmission for the terminals to fit channel capacity of each terminal, and maximize the cell capacity by adjusting the coding rate of channel decoder to control the capability of error protection, and by selecting the suitable modulation scheme to achieve the spectral efficiency.
For example, in communication systems following the third generation (3G) wideband code division multiple access (WCDMA) standard, the CQI reporting is a mandatory feature in the evolution version of the standard, which is named as high speed packet access (HSPA), for the procedure of high-speed downlink shared channel (HS-DSCH) reception. In response to CQI reporting of a terminal, the base station reports information about a transport format resource combination (TFRC) to the terminal; with TFRC, the terminal can reliably receive data from the base station under the experienced or to-be-experienced channel conditions. The TFRC means a communication parameter combination allocating the physical channel resources, including modulation and number of physical channels, and the size of transport block transmitted in the downlink data channel(s). The terminal shall determine the supportable TFRC as the CQI reporting value, and this reporting must be independent of channel variations due to, e.g., the Doppler shift, delay spread and so on. In other words, same values of CQI reporting mean same block error rate (BLER) or same throughput that can be achieved if the base station follows CQI reporting of the terminal.
As a terminal equips a receiver which includes an inner receiver and an outer receiver (a channel decoder), a common quality metric (e.g., SIR, Signal to Interference Ratio or MI, mutual information) reflecting a quality of the communication channel is estimated after the inner receiver and before the outer receiver; however, this kind of quality metric cannot directly reflect the BLER quality and throughput. Moreover, the quality metric measurement depends on pilot part in one physical channel, not the data part in another physical channel; therefore it leads to differences under different channel variations. That is, a fixed mapping relation which directly maps the quality metric to CQI does not generate proper CQI reporting against channel variations.